Drysuit and squeeze question

[NW Dive Dawg]

Please correct me if I am wrong...... but isn't a diver in a wetsuit or even in no exposure suit at all still exposed to that exact same amount of pressure on their chest and back at that depth?

No, you are not correct. The wetsuit compresses, and in fact a wetsuit at about 45 feet of freshwater looses its buoyancy completely (I know, as I took off my weight belt in Clear Lake, Oregon at 45 feet and swam around an neutral buoyancy). So the material compresses, but not against the diver as the pressure on the suit is in both directions (from inside as well as outside), and is therefore equalized. The diver’s lungs are also pressurized by the regulator providing air at the same ambient pressure as the surrounding water. But, you still need to clear your ears; if you don’t then there is extreme pain and a rupture of the ear drum.

SeaRat

Respectfully John, I DO completely agree with you that the wetsuit material compresses from all directions and looses buoyancy, but I still believe my statement above that the diver himself or herself is still subject to the same ambient water pressure that they would be without the wetsuit.

 

[davehicks]

Sure, but in the context of Drysuit squeeze that is not important. What is important is that a sealed and non-equalized drysuit will crush you in a way that a naked diver would not experience.

 

[NW Dive Dawg]

Sure, but in the context of Drysuit squeeze that is not important. What is important is that a sealed and non-equalized drysuit will crush you in a way that a naked diver would not experience.

Totally agree on that.

 

[John C. Ratliff]

Respectfully John, I DO completely agree with you that the wetsuit material compresses from all directions and looses buoyancy, but I still believe my statement above that the diver himself or herself is still subject to the same ambient water pressure that they would be without the wetsuit.

NW Dive Dawg,

I’ve been thinking about this, and the more I think about it, the more I agree with you. There are two dry suit squeezes that I’ve been schooled in, and I did dive a dry suit in the post. I dove the Aquala rubber dry suit. The two types of dry suit squeezes were:

—An ear squeeze, whereby if the hood makes a seal around the ear, the ear drum ruptures outward, toward the external ear canal. The middle ear equalizes to the ambient pressure, but the sealed outer ear does not, and so the ear drum ruptures outward.

—The other squeeze traditionally associated with dry suits, and especially the old style rubber dry suits, is a skin squeeze. The dry suit wrinkles against the skin, and/or undergarments, and pinches the skin. This sometimes in the past caused angry welts on the skin. But this did not cause breathing difficulties. The way around this in the ol’ days before power inflators was to put the mask skirt under the hood, and snort air into the hood, which would then go back into the suit (but not for suits with neck seals).

So what would cause a diver to have difficulty breathing as she was sinking? The video referenced is down, so I cannot comment on that. But I can talk about respiration. Well, a hint could come from the type of breathing the diver does. I, and I think most divers, breath by inhaling for our next breath. But some people, my wife being one, breath differently, by exhaling to their expiratory reserve, and then bring their lungs back to “normal,” thus exchanging air, but from their lower tidal volume. So they are breathing by not inflating their lungs fully, but rather by exhaling and then coming back to “normal.”

Now if a diver was used to this type of breathing, and suddenly started sinking, forgetting to inhale for say 30 seconds, the increased pressure could come close to a lung squeeze and cause considerable difficulty “getting a breath.”

SeaRat

 

[Sebs]

Ok so in a hypothetical situation of extreme suit squeeze that you fear will lead to loss of life, should a last ditch effort be to rip/open the seals to equalise? Or will that cause other problems?

 

[admikar]

If we are talking about Linnea Mills, it would definitely bring whole host of new problems. She was overweight as it is and flooding the suit would only make it worse.
While on it, I still don't buy "can't breathe because of squeeze". I agree with that you can't move, but explanation that pressure differential prevents breathing is red herring IMO. Your body is under same amount of pressure, regardless if it's suit squeeze or air pushing against outside water pressure.

 

[inquis]

I agree with that you can't move, but explanation that pressure differential prevents breathing is red herring

You cannot move because friction prevents your limbs from sliding beneath the fabric or fabric against fabric. Breathing requires *expansion* of the chest cavity with associated sliding of skin and/or fabric. With sufficient pressure differential (aka squeeze), chest expansion/breathing is prevented as well.

 

[KenE]

I believe the biggest misunderstanding about drysuit compression is what is occurring to the drysuit during compression. A neoprene drysuit is flexible when equalized but not flexible when under compression. Take a plastic bag for example, it is flexible when equalized. But now put a vacuum to that same bag and it will turn into a very hard and rigid mass of plastic. The same happens to the drysuit, regardless of material. The vacuum or compression will make the drysuit rigid and very tight against the body (which is 99% water and uncompressible). If you add air to the bag it will return to its normal state of flexibility, same can be said of the drysuit when it is equalized. To be more accurate, take the same bag, add some water, then take a vacuum and see what happens to both the bag and the water. The water is dispersed to small voids in the bag as it is compressed, but the bag and water become very rigid and difficult to move the water around inside. This is basically what is happening to the human body in drysuit compression, a vacuum is occurring inside the drysuit.

 

[Subcooled]

Not friction. Pressure. Your skin and body is almost entirely water and thus non-compressable. Your air spaces in the lungs and sinus become equalized with ambient pressure from the regulator. An unpressurized drysuit gets squeezed down with the full pressure of the water at depth.

So, it will be tight to the skin, but it will not crush you (because you are not compressible, as you said). The suit will be VERY tight, but it will only become a second skin.

 

[Subcooled]

One the other thing, consider a suit that was sealed and filled with water to the max. if it was sealed so that no water could escape, you _wouldn't_ be able to breath, since the lungs couldn't expand as the water in the suit can't compress.

Your breathing capacity would be maybe 30 % but not zero. This is widely experimentally proven in squeeze training/competitions in caving where people actually breathe (laborously) without being able to expand their chest. Enough to survive, enough to cause panic in the uninitiated.